Dear Anand,

Please read the following text:

In theory, calculation shows that 1 kWh is enough to produce one ton of fresh water from seawater. However this assumes a perfect thermodynamic and mechanical system which is not possible to build. In practical terms a desalination system will require 7 to 18 kWh/m3 depending on the corresponding investment.

Desalination systems vapour consumption is usually measured by giving how many kilos of fresh water are produced from one single kilo of steam entering the system. This number, the so-called Gain Output Ratio (GOR), will vary from 6 to 7 for classical plants up to 16 and more for plants equipped with the latest technology.

This figure however does not show properly how steam quality will impact on plant design: the higher the steam supply pressure the more velocity it will provide by expansion, the more suction it will generate and the bigger recovery it will enable thus enhancing overall efficiency. This is why the higher the steam pressure the lower the investment cost for a given GOR. A GOR 8 unit fed with 3 bar steam will cost some 20% more than the same GOR with 20 bar steam.

In addition to steam consumption one has to consider electrical power for pumps. The MSF process requires a large flow of seawater or brine to be circulated in condensers. This results in a specific electrical consumption of 3 to 4 kWh/m3 for MSF plants. This is to be compared to specific consumption of MED plants where no such circulation is required: 1,5 kWh/m3. This is the particular point for which MED now supersedes MSF. By going for MED an Independent Power and Water Company will save some 3 kWh per cubic meter produced: this additional power will be delivered to the network and will generate additional income. This will result in reduced cost of power and water produced by the plant when compared to MSF.

Hoping this will be helpful,

Rafik

I hope it can help

http://www.sciencedirect.com/science/article/pii/S0011916414006857